Four Company of Heroes Mods you must play.

Company of Heroes was, and still is, one of the most interesting RTS games I have played in a very long time. Not only did it include realistically acting infantry squads, but also grant a very "historical" experience. With the Expansions that followed the US and Wehrmacht were supplemented with the Commonwealth and Panzer Elite. Not only were there more campaigns to play through, but the multiplayer experience was enhanced. Here is a list of four published Mods, for this title, which you should absolutely try.
(Company of Heroes, Company of Heroes: Opposing Fronts, Company of Heroes: Tales of Valor, PC)